I use a piece of ¼” tempered glass to make my bridge masks. Lay down few layers of premium 3M masking tape with all the over laps in the same direction

Trace the outline of the bridge

Use a razor or Exacto knife to cut the mask out staying slightly inside the outline. We want the mask to be a tiny bit smaller than the bridge.

Double check to make sure the mask is completely hidden by the bridge. When pulling the mask off the glass lift it under the first layer of tape that was placed on the glass. Otherwise you will pull the mask apart and get the layers out of position.